It must have looked like a scene from Jaws: surfers and sun-worshippers fled Australia’s famed Bondi Beach as the water turned blood red. The alarming hue, however, was not the result of a tragic aquatic accident, but rather came from a crimson algal bloom, ABC News reported.

The beach, in Sydney, Australia, was closed Tuesday while authorities tested the water. According to the Sydney Morning Herald they found that the discoloration stemmed from large floating fields of the red algae, Noctiluca scintillans, or sea sparkle. Although not toxic, swimming in algae-filled water can cause skin and eye irritation because of its high ammonia levels.

Bruce Hopkins, a lifeguard who spoke to the Australian Associated Press, said the bloom had a “reddy-purple” sheen and “quite a fishy smell to it.”

Bondi Beach is one of Australia’s most well-known beaches, and it was added to the country’s National Heritage List in 2008. Nearby Clovelly Beach and Gordon’s Bay were also shut, but the popular spots reopened in the late afternoon when the algae started to dissipate.

A New South Wales Office of Water spokesman told the Australian Associated Press that the red tide was caused in part by an upwelling of colder, nutrient-saturated water. Algal blooms are most common in the spring and fall seasons, as water temperatures are higher and there are “greater movements in ocean currents.” Australia, which is located in the southern hemisphere, is currently transitioning from spring to summer.

On Friday, a toxic bloom was detected in Botany Bay, just south of Bondi, the AAP notes. The New South Wales Food Authority issued an advisory warning against eating “poisoned” shell fish from the bay.

Seaweed removes up to 90% of phosphates and Nitrogen - it also removes many other chemicals including toxins industrial and natural.

The current massive increase in mechanical seaweed harvesting worldwide has led to a major change in the status of the seas. Red tides are always associated with a increase in nutrient levels in the seas.

Organisations caring for bodies of water often have difficulty in associating clean water with the presence of higher plants such as seaweed, the same goes for fresh water.